1. Field of the Invention
The present invention relates to a lens barrel, and particularly, to a lens barrel having a radially-retractable optical element which is capable of radially retracting away from a photographing optical axis position to a radially-retracted position.
2. Description of the Related Art
Generally, in a telescoping lens barrel in which a photographing optical axis is not deflected by use of a mirror or a prism, the length of the lens barrel in the retracted (accommodated) state thereof cannot be made shorter than the total thickness of the optical elements of the photographing optical system in the optical axis direction thereof. Nevertheless, there has been a demand for a further reduction in length of the retracted photographic lens to achieve an extra-short photographic lens. As a solution to this demand, the assignee of the prevent invention has proposed a zoom lens whose length, in a retracted state, is further reduced by radially retracting a part of the photographing optical system away from the photographing optical axis thereof. This zoom lens is disclosed in U.S. patent Publication No. US2003/0156832 A1.
In the above-described zoom lens barrel, a part of the optical system is radially retracted to an off-optical-axis position (radially-retracted position). Accordingly, it is required to position the radially-retractable optical element at each end of the movable range thereof (a photographing position on the photographing optical axis and the radially-retracted position) with high accuracy (precision). If the positional accuracy is low, the optical properties at the photographing position may deteriorate, and furthermore, a larger space may be required in order to allow for overrun of the radially-retractable optical element at each end of the movable range thereof, so that the radially-retracting mechanism would have to be constructed larger in size.